Studies that relate human aggression (including Disruptive Behavior Disorders in children) and suicide to various behavioral and biological factors have been ongoing. The most significant finding is a trivariate relationship among history of aggressive behavior, history of suicidal behavior, and low cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA). The data indicate that certain aggressive, impulsive, and depressive characteristics in childhood are inversely related to CSF 5- HIAA measured during late adolescence. Family instability (particularly alcoholism in a parent) during childhood is also associated with an increased likelihood of aggressive and suicidal behavior in adolescence. Offspring of parents with major affective disorders are more likely to manifest suicidal behavior as adolescents than offspring of control parents. These data, along with the work of other investigators studying aggressive and depressive behavior in childhood, indicate the possibility of traits associated with disordered serotonin metabolism. Further, the consistent relationship between lower CSF 5-HIAA and suicidal behaviors and aggressive behaviors may indicate that some suicidal behaviors are a self-destructive manifestation of a more basic destructive (aggressive/impulsive) trait. A new focus has included the study of early onset substance abusers, both male and female with antisocial characteristics; these studies have now included American Indians and Finns. Related collaborations include PET studies and molecular genetics associated with serotonin metabolism.